1. Field Of The Invention
This invention relates to the field of air pollution control and more specifically to a process and apparatus for the removal of particulate matter and reactive or water soluble gases all of which are known as pollutant material from a stream of polluted carrier gas which may result from the performance of an industrial or chemical process. Thus, the invention relates broadly to a process and apparatus for purifying a polluted carrier gas containing pollutant material such as particulates, gases, vapors or combinations thereof.
Widespread interest in the control of particulates and acidic gases such as sulfur dioxide has been manifested since federal and state legislation relating to polluting emissions was enacted beginning almost ten years ago. Industrial processes such as steelmaking, copper refining, papermaking and others produce gaseous effluents which may contain particulate matter and noxious gases. The particulate matter may be solid or liquid and may vary in both size and chemical composition. With respect to size, the particulate may vary from submicronic particles (particles less than 1 micron in diameter) to relatively large particles which may be a fraction of an inch in size. The chemical composition of the particles depends, of course, on the process involved. While frequently the particulate has no commercial value, there are numerous instances where the particulate, if captured and refined, may yield valuable materials such as iron, zinc, etc. The polluted effluent gases may also vary widely in chemical composition and include relatively harmless gases such as carbon dioxide (CO.sub.2), noxious gases such as sulfur dioxide (SO.sub.2) and hydrogen sulfide (H.sub.2 S), and water soluble gases such as hydrogen chloride (HCl).
Originally, the control requirements for particulate were based upon the weight of the particulate matter, i.e. grains per cubic foot (gr/ft.sup.3) without much concern for the size of the particulate. However, more recently it has been recognized that the large particulate rapidly settles out of the air and is essentially only a local nuisance but that the fine particulate, in the micron and submicron range (1 micron=10.sup.-6 meter) may remain suspended in the atmosphere for long periods of time and cover large geographic areas and thus cause a disproportionate degradation of the atmosphere.
While the relatively large particulate may be readily removed from a gas stream by the use of well-known scrubbers such as cyclone scrubbers or venturi scrubbers, fine particulate is much more difficult, if not impossible, to capture and requires the expenditure of far more energy.
The present invention is particularly directed to a process and apparatus for capturing fine particulate with a minimum expenditure of energy.
2. The Prior Art
The present invention represents a further development of research work begun about ten years ago by some of the present applicants. This work is reflected in several patents including Ewan, et al U.S. Pat. No. 3,852,408; Martin, et al U.S. Pat. No. 3,852,409; Ewan, et al U.S. Pat. No. 3,912,469 and, more recently, Ewan, et al U.S. Pat. No. 4,141,701. In these patents, fine particulate is captured by encapsulating or entraining the particulate in high velocity but small size droplets and thereafter causing the droplets to grow in size until they can readily be separated from the gas in accordance with centrifugal or flow detachment or separation principles.
In addition to the prior art specifically identified in the patents referred to above, Raymond U.S. Pat. No. 467,264 shows an early method of purifying smoke by moistening it with steam and then separating the solid particles centrifugally. Jackson U.S. Pat. No. 723,531 discloses an apparatus for condensing smoke, fumes or gases by the use of a steam jet and a pair of water sprays and separating the particles by gravity or by filtration. British Pat. No. 925,711 discloses a liquid dust filter in which the dust-containing gas is accelerated through a narrowing passage or nozzle and then directed against a liquid stream. Gorman U.S. Pat. No. 3,894,851 utilizes water droplets condensed from steam to mix with a polluted gas. Thereafter, the wetted particulate is separated in a cyclone separator. Barnhart U.S. Pat. No. 3,812,656 discloses a fan driven venturi through which the dirt-laden air is drawn. Water is sprayed into the throat of the venturi to wet the dirt-laden air and the dirt and water separated by gravity while the air is exhausted through the fan. Another form of venturi scrubber is disclosed in Baum U.S. Pat. No. 3,898,308 which provides a series of adjustable water jets at the throat of the venturi.